196 SPECIAL RESULTS IN THE URANOLOGICAL PORTION 



mand, either as the results of observation or of analogy, are 

 not capable of leading to such evidence as other parts of 

 Astronomy enjoy. 



One reason which especially opposes a thorough mathe- 

 matical treatment of problems so difficult of solution, con- 

 sists in our ignorance of the proper motion of a countless 

 host of very small stars (10th to 14th magnitude), which 

 appear scattered amongst brighter ones, and most abundantly 

 in what is so important a part of our sidereal stratum, the 

 rings of the Milky Way. The consideration of our plane- 

 tary sphere, in which we ascend from the small partial sys- 

 tems of Jupiter, Saturn, and Uranus with their respective 

 satellites, to the general solar system, easily led to the Belief 

 that the fixed stars might be imagined to be in an analogous 

 manner divided into many single groups, which, though se- 

 parated by wide intervals, might yet (in the higher relation 

 of such groups to each other) be all subjected to the pre- 

 ponderating attracting force of a great central body, which 

 might be regarded, as it were, as the one central Sun of the 

 Universe. ( 323 ) But the series of consequences here alluded 

 to as having been based on the analogy of our solar system, 

 is opposed by the facts of observation as known to us up to 

 the present time. In the " Multiple Stars," two or more 

 self-luminous heavenly bodies or suns do not revolve around 

 each other, but around a centre of gravity situated far out- 

 side of them. It is true that in our planetary system, 

 something similar takes place, inasmuch as the planets re- 

 volve, not around the centre of the body of the solar orb 

 itself, but around the centre of gravity of all the masses 

 of the system. This common centre of gravity falls, accord- 

 ing to the relative position of the larger planets, Jupiter 



